The present invention relates to heat exchangers in which a fluid passing through a series of tubes is heated by hot gases flowing around the tubes; and more particularly to devices for tieing the tubes together for increased mechanical stability.
As shown in FIG. 1, a conventional heat exchanger 10, such as a boiler, superheater, economizer or air heater, has a chamber 12 through which pass exhaust gases from the combustion process. The gases enter one end 13 of the chamber 12 and flow out of an opposite end 14. A plurality of metal tubes 16 extend across the interior of the chamber transverse to the direction of the gas flow. Depending upon the gas flow direction each tube extends horizontally or vertically with a vertical orientation being illustrated. The tubes are bundled closely to one another in a two-dimensional matrix to maximize the heat transfer. The ends of adjacent tubes 16 are coupled together to form a coil through which water flows. Heat is transferred from the exhaust gases passing around the tubes into the water, converting the water from a liquid state to a gaseous state, or steam.
In industrial boilers, the chamber 12 is very large and the length of tubes 16 relatively long, for example forty feet in length. To maximize the heat transfer, the tubes are bundled closely to one another. The gas flow causes the relatively long tubes to vibrate, which if left unrestricted, causes excessive mechanical wear and generates noise.
To overcome these problems, the vibration is reduced by adding intermediate supports across each line of tubes to provide additional stiffness, thereby inhibiting flow induced vibration. Previously, intermediate tube supports consisted of a metal rod or bar welded transversely to each tube, thereby tying them together across the tube bundle. The supports also maintain even spacing between the tubes 16 by preventing deflection in the midsection of the chamber 12. It is desirable to maintain the tubes in a uniform matrix to provide efficient soot blowing and predictable heat transfer within the boiler. In addition, the tube supports often are used to transmit mechanical shock from a rapper to intentionally vibrate the tubes for periodic cleaning of deposits.
Quite often the exhaust gases from the combustion process are corrosive and attack the metal tube supports. It is not uncommon that the tube supports disintegrate or break loose from the tubes due to the corrosive environment within the chamber. Because of the compactness of the tube bundle and the fact that the supports were welded to each tube, previous supports could not be replaced easily without disassembly of a major portion of the boiler.
It is therefore desirable to have an intermediate tube support which will rigidly hold each tube across the bundle while permitting easy replacement if corrosion occurs.